import java.util.Scanner;
public class ScoreLevel2{
public static void main(String[] args){
   Scanner scanner = new Scanner(System.in);
   System.out.print("please enter student's score:0");
   int score = scanner.nextInt();
   int level= (int)score/10;
   switch(level){
      case 10:
	  case 9:
	     System.out.println("A");
	  break;
	  case 8:
	     System.out.println("B");
	   break;
	   case 7:
	      System.out.println("C");
	   break;
	   case 6:
	      System.out.println("D");
       break;
       default:
          System.out.println("not passed the test.");	   
   }
   }
}